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Comment by whatever1 | Hacker News Reader

Bolts can get unscrewed with vibrations. So probably a design error, they did not use the correct type of bolt (the one with the safety pin).

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Don't they have many ways to prevent bolts from unscrewing? I know at least a few by doing mechanical stuff on motorcycles, and it seems that other planes don't have such problems (at least not within 2 months after the last inspection).

There are washers, or thread lock glue, but it is still a question of correct execution: has the glue been applied? Was the glue batch used before its shelf life? Were the parts degreased before glue application?

Or did anyone decided to cut corners by using an old batch/skipping degreasing/not putting glue because they were late on delivery?

safety wire and cotter pins are preferred methods on aircraft.

Yes. For mission-critical bolts and nuts, absolutely safety wire and cotter pins should be used.

The engineers at Bell also thought that blind bolts you couldn’t inspect in dailies should be wired.

My understanding is that the bolts did have castle nuts and retaining wires in the design. So either they were incorrectly fitted, or the bolts themselves were under specified with regard to strength.

ah. i've been wondering what the method of securing the bolts would have been and have not seen anyone mention it. torque values or threadlocker is rarely enough for the FAA. it's usually safety wire, castle nuts, lock washers, etc.

Not sure what happened from “the design” to “the field”. The two loosen bolts in the picture are not castle nuts.

The door hinge bolt had a castellated nut and pin, but the screws holding the hinge mount to the airframe apparently had no retaining wire. See leaked photo at: https://twitter.com/ByERussell/status/1744460136855294106/ph...

Those bolts aren’t drilled for safety wire.

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